Skip to main content

Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

See other formats



out with about 300 c.c. of water in all. The whole is then evaporated on
a water-bath to about 50 c.c., and filtered, the filter being washed with
hot water ; the filtrate is acidified with hydrochloric acid and the sulphuric
acid precipitated as barium sulphate : BaS04 X 0-1374 = S.

This method is also applicable to all derivatives of crude petroleum and
always gives good results.

4. Determination of the Solid Paraffin.—This is effected by Holde's
method, after fractions below 300° have been eliminated. To this end,
100 grams of the crude petroleum are rapidly distilled, the distillate up to
300° being collected. If the residue from the distillation is dark and turbid,
as is usually the case, it also should be distilled—the thermometer and
condenser having been removed—until only fixed, carbonaceous residue
remains in the retort. The distillate above 300° for the oil remaining in
the flask if it is not distilled) is weighed and treated as follows in the appara-
tus shown in Fig. 42.

This consists of a vessel surrounded by felt and containing an ice-salt
mixture in which are immersed the tubes containing
the test material and the funnel used for the filtration ;
the funnel is connected with a pump flask. The ap-
paratus is provided with another tube (5) by means of
|f which the water from the freezing mixture may be
run off.

Of the oil distilled as described above, 5—10 grams
are placed in a wide test-tube and dissolved in the
necessary quantity of a mixture in equal proportions
of absolute alcohol and ether. The tube is placed in the
freezing mixture so as to keep it at about — 20°, and,
while the liquid is stirred with the thermometer, the
alcohol-ether mixture added until the oily drops which
separate are redissolved and only the solid paraffin
remains out of solution. The liquid is then filtered by
means of a pump on the funnel kept between —15°
and —20°, the residue being washed with cooled
alcohol-ether mixture (if the solid paraffin is soft, it is well to wash with
a mixture of 2 parts of alcohol and one of ether) until a few c.c. of the washing
liquid leave no appreciable oily residue on evaporation. The remaining
solid paraffin is then dissolved on the filter in hot benzene into a tared glass
dish, the benzene being evaporated on a water-bath—which finally should
boil vigorously—and the dish dried for 15 minutes at 105°, cooled in a
desiccator and weighed. The percentage of solid paraffin in the original
oil is then calculated.

By this method, a small quantity of solid paraffin remains dissolved in
the alcohol-ether mixture ; the result obtained should, therefore, be increased
by 0-2% for a very fluid oil, or by 0-4% for an oil so rich in solid paraffin
that it deposits it at 15°.

5. Detection and Determination of the Asphalt.—Usually two
varieties of asphalt are distinguished in crude petroleums, namely, hard
and soft asphalt.

FIG. 42rough about